Telephone call transmitter



Jan. 6, 1948. 1.. J. BOWNE TELEPHONE CALL TRANSMITTER 8 Sheets-Sheet 1 Filed April 4, 1945 r (5 m J a o Y INVENTOR LJBOWNE 4 amt MA ATTORNEY Jan. 6, 1948.

L. J. BOWNE TELEPHONE CALL TRANSMITTER Filed April 4, 1945 8 Sheets-Sheet 2 A 7 TORNEY Jan. 6, 1948. BOWNE I 2,433,836

TELEPHONE CALL TRANSMITTER INVENTOR LJBOWNL ATTORNiV Jan. 6, 1948. ,1. BOWNE TELEPHONE CALL TRANSMITTER Filed April 4; 1945 8 Sheets-Sheet 4 Rat En //v l/E/V TO R L .J. BOW/V15 Bk: 4. a m

A T TOR/VEV Jam. 6, 1948. L. J. BOWNE TELEPHONE CALL TRANSMITTER 8 Sheets-Sheet 5 Filed April 4, 1945 aohun+nux INVENTOR L. J BOWNE 4 a 14%- ATTORNEY Jan. 6, 1948. 1.. J. BOWNE TELEPHONE CALL TRANSMITTER Filed A rii 4, 1945 8 Sheets-Sheet 6 INVENTOR L. J. BOWNE '4 a m A T TORNEV Jan. 6, 1943. L, J. B WNE 2,433,336

TELEPHONE CALL TRANSMITTER Filed April 4, 1945 8 Sheets-Sheet 7 lNl/EN TOR L. J BOWNE A TTORNEV Jan. 6, 1948.

L J. BOWNE TELEPHONE CALL TRANSMITTER Filed April 4, 1945 8 Sheets-Sheet 8 I INVENTOR L.J.B0W/VE m 6R T 3 an F 9* s32! use p h. .F Pl KR M V Wig QM W [3M8 L ma v 1 K 9% S RN A1 $2395 1 \r b b L n an H h 7 l NQN) R L v w P8 MM 3w 9% kw 1 N RN flm mum T LT NSUSPgQ F v HI L Y PKWN WDw \\N 1 H L 1 WWW I" P I: l QM. E Qw a 7 FA? 6w 7 P31 m 0% A TTORNEY Eatented Jan. 6 1948 TELEPHONE CALL TRANSMITTER Langford J. Bowne, Howa1-d Beach, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 4, 1945, Serial No. 586,560

9 Claims. (Cl. 179-90) This invention relates to telephone systems and particularly to central office, or private branch exchange telephone systems of the type in which subscribers stations, having normal access to the exchange equipment in the extension of calls originated at the stations, are provided with additional facilities whereby direct communication connections between the several stations of the system may be initiated expeditiously and with a minimum of effort on the part of the subscribers thereat, and maybe completed without routing the calls through the central office, or private branch exchange.

Systems of communication of the above-indicated character are generally known as key calling telephone systems in that connections between calling and called stations of the system may be initiated at any of the stations by simply actuating a key, or button, at the calling station assigned to the desired called station.

It is the object of this invention to provide an improved telephone system of the key calling type.

This object is attained in accordance with a particular feature of the invention by characteri'zing each of a plurality of station-identifying code signals by a different combination of three current impulses of positive, and/or negative polarities, and by the provision of preset means at the subscribers station for predetermining the character of each of the three code impulses, and

the necessity for the originating, or adding subscriber to restore the telephone to its support. More particularly, during the existence of a connection between any two subscribers stations, either subscriber may actuate a key, or button corresponding to a third station to prepare the transmitter at the station for the transmission of the code signal which identifies the third station, and then operate key means which simulates the removal of the telephone at the station in causing the transmitter to'operate'and transmit the code of the third station.

A still further feature of the invention resides in the'provision of means whereby a connection extending from any station and involving a central office or private branch exchange line may be held by transmitting from the station a predetermined code'signal. More particularly, a hold key is provided at each of the stations and functions to transmit a predetermined group of code impulses which selectively control the connection of a holding bridge to the central ofiice, or private branch exchange line.

Still another feature of the invention provides facilities whereby a subscriber may hold a connection on a central ofiice, or private branch exchange line, and thereafter selectively complete of means which function, incident to the removal of the telephone from its support at the Calling station, to consecutively transmit the precharac- .terized impulses over the calling line to control the completion of a connection from the calling station to the called station identified by the consecutively transmitted code impulses.

More particularly, this feature of the inven= tion contemplates a code signal transmitter of the dry rectifier type, and means embodied therein and selectively controlled by any of a plurality of manually operable station-identifying keys, or buttons, for preparing the transmitter for the transmission of a preselected code corresponding to the operated key, and other means for rendering the transmitter operable, to transmit the preselected code, in response to the removal of the telephone from its support subsequent to the actuation of the code selecting key, or button.

Another feature of the invention contemplates facilities whereby a false or incorrect setting of the code transmitter may be corrected prior to the removal of the telephone handset from its support at a call-originating station.

A further feature of the invention provides facilities whereby conference connections may be originatedat any of the stations of the system, or additional stations may. be added toan already existing connection between two stations without a communication connection between his station and any other station of the system, and may also be a party to a conference connection for the period during which the central office, or private branch exchange connection is held.

Another feature of the invention precludes the possibility of losing a central office, or private branch connection in the event of accidental operation of the switchhook contacts after a call to the central office or private branch exchange has been initiated.

Other features of the invention contemplate novel circuit arrangements which render possible the realization of the features individually set forth above. In accordance with one such other feature, a pyramidal arrangement of selectively operable line-connecting relays is resorted to, the relays of which functionunder control of the code transmitters at the several stations of the system to selectively interconnect the line circuit of any calling station and the line circuit of any of a plurality of called stations. More particularly, each of the relays of the pyramidal arrangement of line-connecting relays comprises two separately energizable windings, each of which is selectively controllable from one of two different stations to extend a calling line to a called line. Each double winding line-connecting relay is assigned to two stations and is controlled therefrom in such a manner that when a first station ori inates a call to a second station the relay operates over one winding incident to the operation, at

the first station, ofa key, or button, allocated. I

,3 to the second station, and when the second station originates a call to the first station the relay operates over its other winding incident to the operation, at the second station, of a key, or

button, assigned to the first station, and when operated over either winding, functions to interconnect the line circuits of both stations. Thus, the number of line-connecting relays for a system involving a predetermined number of stations is determined by the formula where n is the predetermined number of stations. For example, in a system involving eighteen stations, the number of line-connecting relays required is one hundred fifty-three.

A still further feature of the invention contemplates thesignaling of a called station substantially instantaneously with the seizure of the called line and to thereafter continue signaling the called station on an intermittent basis. This feature is obtained by means of a ringing control circuit comprising a single relay, a resistance and a thermistor, and a local source of alternating current, the elements of the ringing control circuit being so disposed relative to one another that, upon the operation of the relay to connect the alternating current source to the called line, the resistance is connected in parallel with the thermistor and the relay winding to reduce the current flowing through the thermistor. The thermistor accordingly cools off so as to prevent sufficient current to traverse the relay winding. The relay then releases and opens the resistance shunt thereby permitting sufiicient current to again traverse the relay winding through the thermistor to cause the relay to operate. This cycle of operation and release of the ringing relay is. repeated and the alternating current source is intermittently connected to the called line in a manner that simulates machine ringing and precludes the delay in the operation of the ringer at the called station which occurs when the ringing relay operates on the silent interval.

These and other features of the invention will be best understood from the following detailed description when read in connection with the accompanying drawings, in which:

Fig. 1 is a perspective View of a telephone set illustrating the location of the various reset, hold and station-selecting buttons thereon. If desirable, the reset and hold buttonsmay occupy positions other than those illustrated, for example, the reset button may be located on one side of the set and the hold button to the right or left of the dial;

Fig. 2 is an end view of the telephone set shown in Fig. 1 with a portion of the side wall of the casing broken away to expose the transmitter mechanism housed within the casing. In this view the mechanism is depicted in its normal condition and with the telephone handset on its cradle support;

Fig. 3 is a view similar to that of Fig. 2 showing one of, the buttons depressed and the handset partially lifted from its support;

Fig. 4 is a fragmentary view of the transmitter control mechanism which is operated incident to the removal of the handset from its support. In this view the handset has been completely removed from its support;

Fig. 5 is a plan View of the code transmitter mechanism;

Fig. 6 is a view of the reset control mechanism prior to the operation of the reset button;

Fig. 6A is a View similar to that of Fig. 6 show ing the reset control mechanism inits operated condition;

Figs. 7 and 7A are views illustrating the manner in which the buttons are mounted, and the latching and releasing mechanisms therefor;

Fig. 8 is a detail view illustrating the means employed for maintaining the code transmitter camshaft in its normal position and for insuring the shaft comingto rest in that position after its cycle of operation;

Fig.9x is a chart showing the various codes resultingfrom the operation of the buttons, and the bar contacts whose operation determines the code;

Fig. 10 is a wiring diagram illustrating in simplified schematic form the line-connecting and control circuits involved in the key-telephone system of this invention;

Figs. 11, 1-2, 13 and 14, when assembled in the manner indicated in Fig. 15 constitute a detailed disclosure of the circuits involved in the keytelephone system of this invention; and

Fig. 15 is a block diagram showing the manner in which Figs. 11, 12, 13 and 14 are to be assembled to effect a complete showing of the circuits involved in the system of this invention.

Before entering into a detailed description of the code transmitter utilized at the several stations of the telephone system of this invention illustrated in the drawings and of the operation of the system, a brief reference will be made to Figs. 11 and 10 of the drawings. Fig. 11 includes a schematic illustration of the code transmitting mechanism while Fig. 10 is a schematic wiring diagram showing in simplified form an over-all picture of the system.

The essential elements of the code transmitter are schematically shown in Fig. 11. It consists of a rotatable camshaft 203 having fixed thereto, in spaced relation, three pulsing cams Pl, P2 and P3; a. pulse on cam PO; an off normal cam PON;. a single-toothed ratchet wheel or disc 22l; and a cam 231 having a portion of its periphery flattened'tocooperate with a flat spring 236. The cam 23! and its associated spring 236 functionto assure the cam shaft coming to rest in its normal position after operation, and to hold it in this position. The left end of cam shaft 203 is hollow so as to accommodate a projection of the gear'wheel-meshing with a geared sector 2l9. A motor spring 202 has one end fixed to the gear wheel and the other end fixedto the ratchet wheel 22L The cam shaft 203 is normally held against rotation by the pawl 220 which engages the single tooth of the disc 22 I.

When the geared sector 2l9 is actuated in a manner to be subsequently described, energy is stored in the motor spring 202, and when the handset 200 is removed from its mounting, the linkage shown betweenthe handset button and the pawl 220 functions to disengage the pawl from the disc 22I whereupon the cam shaft 203 makes a complete revolution under the action of the motor spring 202.

The off normal cam PON is provided with a single notch which accommodates the stud controlling the contact springs SON when the cam shaft is in its home position. The cam PO is providedswith four notches, l., 2, 3 and the home position notch, spaced degrees apart on the cam periphery. Each of the cams Pl, P2 and P3 is provided with a single cam lobe, the three lobes being respectively displaced 90 degrees so that they function in sequence to operate their respective pulsing springs SI, S2 and S3, The" selector sideby corresponding springs A, B, C, D,

E and F, which are individually controlled by the code bars AI, BI, C2, D2, E3 and F3, respectively, which code bars, in turn, are operated in various combinations under control of the keys, or buttons,'designated H and 2 to 18, inclusive; The combination in which the code bars are operated in response to the actuation of any of the keys, or' buttons, is indicated by the small circles appearing at the points at which the code bars cross the lines extending from the keys. For example, when key, or button, 9 is actuated, code'bars AI, D2 and F3 are actuated, in turn operating springs A, D and F. Thus, when any one key or button, other than the reset button RE is actuated, one or moreof the dry rectifiers has its individual short circuit removed by the operation of the cor responding springs A, B, C, etc.

As the cam shaft 283 starts its clockwise rotation under the action of motor spring 202, the springs SON immediately are operated to short the telephone equipment and to connect the tip conductor of the station line L to the ring conductor thereof through the springs SI, S2, S3 and SO, though the last set of springs, also operating at the start of rotation of the cam shaft, renders this connection open. When the cam shaft has rotated 90 degrees, the lobe of cam PI functions to separate the springs SI and simultaneously, the stud associated with the springs SO drops into notch I of cam PO. Atthis interval, therefore, the circuit from the tip conductor of the line L extends through the alternate contacts of springs 2M and SON, conductor 223, through rectifiers a and b if both springs A and B are actuated, or through both springs A and B if neitheris actuated, conductor 222, springs S2, S3 and S0, to the ring conductor of line L. Thus, in the first signaling position of shaft 203, either one or the other, or both rectifiers a, b are eflectively included in the signaling circuit involving the conductors of line L and determine the character of the impulse transmitted thereover during this interval.

As the shaft 203 moves out of its first position, the stud associated with springs SI functions to reclose the springs while the stud'associated with springs SO moves out of the notch I in cam PO to open the springs SO. Thus the signal transmitting circuit is restored to its original condition, that is, with all dry rectifiers short-circuited on the transmitter side and the signal path open at the springs SO. in the second position of the cam shaft 233, the springs S2 are opened and the springs SO are closed so that the character of the signal impulsetransmitted is determined by which, if any, or both of the rectifiers c and d have their short circuits removed by sprin s C and D; Similarly, for the third position of the cam shaft 203, the'springs S3 function to remove the short circuit from the third group of rectifiers e and 1, so that an impulse, depending-for its character-upon whether or-not any ofthe-two springs E and F is actuated, will be transmitted over the line L, The cam shaft comes to rest in its home position and the station circuit is reconnected to the'line and the transmitter efiectively disassociated therefrom.

The character of the code impulses consecutively transmitted by the transmitter incident to the actuation of the keysor buttons H, 2 to 18, inclusive, and the corresponding operated code bar contacts, are shown in the chart of Fig. 9.

The key or button designated RE in Fig. 7' is a reset button and its function will be described in detail hereinafter.

Fig. 10 discloses five subscribers stations each of which is equipped with a telephone handset on the base of which is mounted eighteen buttons or keys. In this showing only eighteen buttons are shown as a matter of convenience. The single heavy line conductors are intended to represent the tip and ring conductors, or the communication channels extending from eachstation and which are adapted for interconnection by the various double winding line-connectingrelays shown. The rectangles designated REG are intended to represent the signal receiving and register circuits individually associated with each station.

Extending from each rectangle REG are eighteen conductors which, incident to the actuation of the buttons H and 2 to 18, inclusive, at any station are grounded to complete an energizing circuit for one or the other windings of the lineconnecting relays, such as relays 24I, 252, 253, 332, 348 and 33I. Relay 2 is common to both stations Nos. 1 and 2, its upper 1-2 winding beingcontrolled by button No. 2 at station No. 1 and finds battery in the line circuit No. 2, so that when energized by way of its upper winding, relay' 24I functions to interconnect line circuits Nos. 1 and 2, with station No. 1 being the calling station and station No. 2 being the called station. Similarly, the lower 2-1 winding of relay 2:" is controlled by button No. 1 at station No. 2 and finds battery in the line circuit No. 1, so that when energized byway of its lower winding, relay 24I again functions to interconnect line circuits Nos. l and 2, with station No. 2 being the calling station and station No. 1 being the called station.

Each of the other double wound pyramidal lineconnecting relays is similarly common to two stations, relay 252 being common to stations Nos. 1 and 3; relay 253 to stations Nos. 1 and 4; relay 332 to stations Nos. 2 and 3; relay 348 to stations Nos. 2 and 4; relay 33I to stations 3 and 4, etc. As will appear from a later description, the operation of any line-connecting relay'will be followed by the operation of corresponding cut-- through relays such as relays 228, 243, 322, etc.

Extending from each register circuit REG is a conductor designated X. This conductor is groundedincident to the actuation of the hold button or key at each station, thatis, the lead X from the register circuit REG associated with station No. 1 will be grounded when the hold button H at station No. 1 is actuated; the lead X from the register circuit REG associated with station No. 2 will be grounded when the hold buttonH at station No. 2 is actuated; etc; The

grounding of any of these leads will serve to operate a relay in the hold circuit, such as relay 580 of Fig. 13 which functions to place a hold condition on the central ofi'ice, or private branch exchange line, as will be fully described hereinafter. i

Normally,- the-line extending from each station,

isextended to the centraloflice, :or private branch exchange line over back contacts of corresponding cut-through relays 228, 243, 322, etc. so that when the telephone handset at astation is removed from its support without a stationselecting button having been previously operated, the connection is made in the .usual manner through the central ofiice, or private branch exchange.

While but five stations are shown in Fig, 10, it isto be understood that the station capacity of thesystem is not so limited.

The description immediately following is dirooted to the mechanical structure of the codetransmitting mechanism, and for this purpose particular reference is made to Figs. 1, 2, 3,. 4, 5, 6, 6A, 7, 7A and8.

The base of the telephone set is identified by the numeral 2|] and supports the cover or casing 2| in the well-known manner. Near the rear of the base and secured thereto by means of screws 22 is a mounting bracket 23. This bracket isprovided with a plurality of inwardly projecting arms 24, 25, 26 and 21 as clearly disclosed in Fig. 5. These arms constitute supports for two shafts 28 and 29, the latter being relatively short and supported in suitable apertures in the bracket arms and 26. The shaft 28 which is considerably longer than shaft 29 is supported in suitable apertures in the bracket arms 24 and 2'! and, as shown in Figs. 2 and 3, is located above and slightly forward of shaft 29. The elements which are carried by these shafts and their functions will appear as the description progresses. These shafts are prevented from longitudinal shifting by means of lock; rings carried thereby externally of the supporting bracket arms.

A pair of brackets 36 and 3| which occupy positions at right angles to the longitudinal span of bracket 23 are fixed to the base 20 by means of screws 32 and is provided with two verticallyextending arms indicate-d by the numerals 33, 34, and 36. Between the bracket arms 34 and 35 is mounted a two-piece shaft, the two portions of which are designated by the numerals 31 and 38, respectively. The shaft 38 is relatively long and at its inner, or left end viewing Fig. -5, is provided with a relatively short axial bore into which the right end of the shaft portion 31 is adapted to be journaled for rotational movement relative to the shaft portion 38. The shaft portions 31, and 38 are also provided with lock rings 40 and with fixed collars 44 to prevent longitudinal shifting thereof.

The shaft 31 supports a pinion gear 4|, a ratchet wheel 42 and a disc 43 allof which elements are free to rotate on the shaft. The pinion 4| and the ratchet wheel. 42.are integrally formed so that any rotational movement experiencedby the pinion is similarly experienced by the ratchet wheel. The rotational movement of pinion 4| and ratchet 42 in one direction is communicated to the disc 43 through the pawl 45, which, as clearly shown in Figs. 2 and 3, is pivotally carried by the disc near a point at its edge and is biased in thedirection of the ratchet wheel by means of the spring 43. Thus when the ratchet wheel 4| is driven in a counter-clockwise direction under control of a geared sector 2| 9, as will be described more fully hereinafter, the disc 43 is similarly rotated.

The disc 43 'is spring-coupled to thegear-22| by means of a motor spring 202, one end of which isg s to xand he henend ic isfixed to the gear. 22|. The .gear'22|' is providedwith acollar orflangewhich is pinned to shaft 338 .so. as to, fix the gear thereto. A tripping pawl 220 ,is carried on the shaft 29.and is heldin enga ement with the single tooth of the disc 22L The pawl 220 is an integralextension of a substantially U-shaped member 60, the two inwardly projecting arms of which are apertured to permit the passage of shaft 29 therethrough. A spring 6| whose ends bear respectively onthe bracket arm 26 and the right arm of the pawl, member 60 serves to normally bias the. pawl 22fl in a direction such as to insure engagement of the pawl with the gear 22].

In thenormal position of the code-transmitting mechanism as shown in Fig. 2, the gear or disc'22l isheld against counter-clockwise rotation by the influence of the pawl 220 so that when the sector; H9 is actuated to drive the pinion 4|, the disc43 rotates, carrying with it one end of the motor spring 202, the other end of which is fixed. to disc 22|, and since the disc 22| is restrained from rotating by pawl 220, the motor spring 202 is wound up and stores sufficient energy-to drive the shaft 38 when the pawl 220 is tripped in a manner to be described hereinafter.

The shaft 28, which hereinbefore has been described as being mounted in suitable apertures in the bracket arms 24 and 21, pivotally supports asubstantially U-shaped member 52 having two depending arms 53 and 54, the former being considerably longer than the latter, as clearly appears in Figs. 2 and 3. On the outer face ofarm 54. is pivotally mounted a spring-biased latching pawl 55 which serves as a latch to maintain the geared sector 2|9 in its operated position, as shown in Fig. 3. When the geared sector 2|9 is raised to its operated position, the free end of the latching pawl 55 is forced by the action of spring 56 into the notch 51 on the inner peripheral edge of the sector H9 and holds the sector in its operated position.

As will be described presently, the pawl member 60 with its integrally-formed pawl 220 is tripped to effect the release of the disc 22| under two conditions, one in response to the removal of the telephone handset 200 from its support, and the other in responseto the operation of the reset button RE. Similarly, the pawl 55 which functions to lock the geared sector H9 in its operated position is actuated to release the sector at a predetermined time in the operation of the code transmitter. This release operation of the pawl 55 occurs near the end of the code-transmitting period and is effected by the engagement of a cam with'the lower end of the arm 53. as will be described presently. Suffice it to say at this time that the lower end of arm 53 is forced forwardly by the .cam so as to cause the member 52 to pivot in a counter-clockwise direction on the shaft 28. Thu theintegral arm 54 thereof is moved upwardly carrying-with it the pawl 55, it being understood that a stop pin 58 propels the pawl out of engagement with the notch 5l-inthe geared sector 2E9. v

The. shaft 38 has keyed thereto aseries ofcams identified as PON, P0, P3, P2, PI, 62 and 231. When the pawl 223 is tripped subsequent to the winding up aof themotor springZlJZ, theenergy stored in the spring is released and utilized to drivethe shaft 38 through one revolution. It will be understood that whenthe pawl 22U-is tripped, thegeared sector 21.9 is still locked by the latching pawlo55- so that the pinion ;4 andits integrallywith the contact springs 20!.

formed ratchet wheel 42 and the disc 43 are held stationary so as to permit the energy stored in the -motor spring 202 to be expended in driving the shaft 38 to which the above-identified cams are pinned. Mounted on the bracket 23 in cooperative association with the cams PON, P0. P3, P2

and PI are the contact springs SON, S0, S3. S2 and SI, respectively. As described in connection with the schematic showing of the code transmitter in Fig. '7, and as will appear more fully in the circuit description to be made hereinafter, the cams function during their rotation to actuate their corresponding contact springs.

The cam 231 is provided on its peripheral edge with a fiat section against which the flat spring 230 abuts as shown in Fig. 9. This cam-spring combination assures the shaft coming to rest in its normal position. The spring 236, as illustrated, is mounted on the base 20 of the telephone set.

The cam 62, which as shown in Fig. 5, is peripherally aligned with the arm 53 of the U-shaped member 52, is provided with a camming lobe 63 which is so positioned on the cam periphery that it functions during the last one-quarter revolution;

of the cam shaft to actuate the arm 53 and cause it to disengage the pawl 55 from the geared sector 219 so as to allow the. latter to restore to its normal position under the action of spring -66 which is engaged by the bracket 63 mounted on:

the common bar 61 with which the geared sector -2l9 is integrally formed, when the common barls actuated together with any of the code bars Al, -Bl, C2, D2, E3 and F3. mounted on the base of the telephone set which- At 50 is shown a stop springs which are operated to effectively include the station telephone apparatus in the line circuit when the handset is removed from its support. At its outer end the bracket arm 12 pivotally supports a lever 15 having one end interposed between the button 206 and the stud 11 associated When the handset is positioned on its support, its weight serves to depress the button 206, which through the lever 15 and the stud 11 maintains the contact springs -l in disengagement. When the handset is removed from its support. the lever 15, under the ction of spring 18 and the tension of the contact springs 20L raises the button 206 and permits the contact springs 20! to move into engagement.

The outer end of lever 15 is provided with an irregular peripheral edge, one face of which normally engages a roller 11 which is rotatably mounted on the extreme end of the lever 19. The lever 19 is formed by riveting together two projec tions of complemental parts 80 and 8|, which together form a substantially U-shaped element having two short arms at its extremities which are suitably apertured to receive the shaft 20. As

shown in Fig. 5, the left end of this element, or of the complement-a1 portion 8| thereof, is provided with a collar 82 which is pinned to the shaft 28. Also at its left end the portion 8! is provided with an integral hook-shaped projection 83 which'normally abuts the tripping pawl member 60-with which the tripping pawl 220 is integrally formed.

Thus, when the telephone handset 200 is removed from its support, the lever 15 moves in a clockwise direction about its pivot causing lever 19 to move similarly about the shaft 28 so that the projection 83 of the lever acts upon the member 60 to cause the tripping pawl 220 to move out of engagement with the disc 22! thereby freeing the cam shaft 203 for rotation under the action of motor spring 202. Thus the shaft 203 is rotated, carrying with it the cams PON, P0, P3, P2, PI, 62 and 231, the second last of which, cam 62, functioning, as previously described, during the last quarter cycle of rotation to actuate lever arm 53 and to thereby cause the disengagement of the latch pawl 55 from the geared sector 2I9 to permit the sector 2H) and its integrally-formed common bar 61 to restore to normal. It is to be understood that the 'motor spring 202 will be so adjusted that the energy stored thereby, when the spring is wound up, is sufiicient to insure a complete revolution of the cam shaft 203. As the shaft reaches its home po sition, the energy in the motor spring will be sufficiently expend-ed so that the engagement of spring 236 with the flat surface of cam 231 will insure the shaft coming to rest in its home position. The arresting of the shaft in this position is further insured by the dropping of the stud associated with the springs SON into the home position notch in cam PON. The pulsing cams Pl, P2 and P3 will'have functioned during the first three quarters of the'shaft revolution to actuate the springs SI, S2 and S3 in sequence.

Fig. 3 illustrates the position of the levers 15 and 19 when the handset-button is half-way projected from the casing 2|. In this position the pawl 220 will have been tripped and the cam shaft 203 will have started its cycle of rotation.

When the handset 200 is completely lifted from its mounting, the relative positions of the levers 15 and 19 will be asillustrated in Fig. 4. The contour of the camming end of lever 15 is such that the lever 19 occupies the same positions with the telephone handset on its support and with the telephone handset fully removed. This is necessary since the code transmitter must function to transmit code signals in response to the removal of the handset from its support, and must also be capable of transmitting code signals with the handset already removed from its support in the event it is desirable to add other stations to an already-completed connection in the case of conference calls. Therefore, with the lever 19 in the position indicated in Fig. 4, the pawl 220 will be positioned so as to reengage the-tooth in disc 22I at the end of the rotation ofthe cam shaft to thereby render the transmitter operable to transmit code signals while the handset is removed from its support.

'In the event that a subscriber has actuated a station-selecting button improperly, that is, if button No. 2 is actuated when button 'No. 3, for example, should have been actuated to initiate a desired connection, provision is made to reset the transmitter before the handset is removed from its support and thereby render void the original setting of the transmitter. To provide for this contingency, all of the buttons mounted onthe telephone set, with the exception of the reset button RE, are provided with means for latching them in their operated positions and other means, to be described presently, are provided for restoring the transmitter to its normal position.

As shown particularly in Figs. 2 and 3, a boss l00 depending from the underside of the casing 2| just above the position occupied by the buttons 11 has-secured -to-itslower face-,by'screws I a plate 402; This s plateisprovided with suitable apertures through-whichthe lower shank portions'ofthe'buttons freely pass and constitutes one of three substantially similar plates which are mounted in superposed relation as a unit by means of screw bolts I03 and suitably-dimensioned spacing collars I04.- The middle plate I05 is-a latchplate provided at each end with a slot I06 which permitsthe'plate'to slide longitudinally a limited amount on theupper edges of the lower collars I04. A spring I01 having-one end fixed to the uppermost stationary plate I08 and the other end fixed to the slidable plate I 05 normally biases the latch plate to the left, viewing Figs. '7 and 7A. Eachkey-or button other than reset button RE, is provided with a camming area on its shank which serves, when any of these buttons is depressed, to move the plate I05 to the right against the action of spring I01 until the camming portion of the key shank has passed through its corresponding hole -in the latch plate, when the spring I0'I functions to restore the latch plate so that the upper edge or shoulder of the camming portion 'of the key impinges against the underside of the latch plate.- In this manner any of the keys, other than reset'key RE, is effectively locked in-its depressed position" when manually moved thereto.

Dependingfrom the latch plate I05 near its left endis a cam projection I09 which is adapted to be engaged by the projection IIO, fixed to the left end of thecommon bar 61, in such'a manner that when the common bar is restored to normal,

as will be described, the projection II 0 in moving 1 upwardly engages, with a camming action, the projection I09 causingthe latchplate I05 to be moved to its unlatching position and thereby effecting the release of the depressed button.

Each button is provided with a coil spring III- which is woundaround the lower shank-portion of thebutton and-is confined between a collar IIZ and the upperface of the stationary plate I02, I This spring-together with the return of the operated-code barsserves to restore the button when unlatched.

The reset button RE is of the non-locking type and' is normally held-in its unoperated position by the spring III.- When depressed,- this key engages the extension I I2 of a substantially Z-shaped member I I3 which is pivotally mounted on theshaft I I4. The shaft I I4 is carried in suitable aperturesinvertical extensions of bracket 30'and bracket I I5, the latter of which is fixed to the base20-by means of screws and cooperates withaforward extension of bracket 3| in furnishing a support forthe spring 65, which spring, as previously mentioned. is engaged by the common bar 61 when the latter is actuated and serves to assist in restoring the common bar to normal. The inwardly projecting arm of the Z-shaped member II3, which is identified on the drawings by the-numeral II6,-has its inner end arcuately shaped so; as to function as a cam in actuating the arm I H; which, in turn. is pivotally mounted on the -shaft 28. A hook-like projection IIB extends from the underedge of the arm I" and makes contact wit-hthe pawl member 60 which, as previously-described, has integrally formed therewiththe tripping pawl 220.

When the reset button RE is actuated subsequent to the depression and locking of a stationselecting button and prior to the lifting of the handset 200 from its support, the lower face of the button- RE' engages the projection H2 and; de-

presses it. The inwardly-projecting cam arm IIB of the Z-shaped member II3 moves upwardly from the "position shown in Fig; 6 to the position shown in Fig. 6A, and in so doing, cams the arm II! in a counterclockwise direction. The hooklike projection II8 of arm II'I accordingly functions to lift the tripping pawl 220 out of engagement with the tooth of disc 22I thereby freeing the cam shaft 203- and' permitting it to rotate under the-action of motor spring 202. Since the telephone'handset is not removed from its support at this time to operate switchhook springs 20I, the operation of the code-sending springs by their respective cams does'not result in the transmission ofa code signal over the line. When the code-transmitting mechanism completes its cycle, the geared sector 2I9 of the common bar 61 is released in a manner previously described and under the action of springGB restores to normal position. As the bar 61 approaches normal position, th projection IIO thereon engages the latch plate arm I09 to move the latch plate I05 to its unlatching position whereupon the previouslyoperated and locked button restores to its normal position under the action of its corresponding spring III.

The six code bars AI, BI, C2, D2, E3 and F3 and the common bar 61 are-pivotally carried on shafts H4 and I20,- the latter being supported in suitable apertures in an extension of bracket 3I and in the bracket I,2I. Suitable collars are interposed between the code bars and their supports to maintain them in fixed-spaced relation. Each of the inwardly-projecting right-hand extensions of the c'ode'bars is provided with an integral spring-operating projection I22 which serves to operate the springs A, B, C, D, E and F when the corresponding code bar is actuated. These springs, as'previously described, operate to remove short circuits from the dry rectifiers a, b, c, d, e and Each code bar is provided with short, integral substantially vertical projections I30 which are disposed immediately below the buttons H, 2, 3 to 18 mounted on the telephone set. The number of projections I30 on each code'bar is'de'termined by thenumber of buttons which operate the code bars. As indicated in'Fig. '7, code bar Al, for example, is'p'rovidedwith nine spaced projections so that this code bar is actuated when anyone of buttons H, 3, 5, 7, 9, 11, 13, 15 and 1'? are depressed. In cases where one button functions to actuate more than one'code bar, the projections I30 extending from such code bars are provided with right angular oifsets so as to render the plurality of bars operable by a single button, as shown in Figs. 2 and-3. The common bar 61 is so disposed relative to the six code bars that it is operated whenever any one of the code bars is depressed. In other words, the common bar '61 is actuated whenever any one of the buttons H, 2, 3 to 18' is operated.

The contact springs A, B, C, D, E and F are suitably mounted on the base of the. telephone set as clearly shown in Fig. 5, and also in Figs. 2 and-3 Operation of the code transmitter When it is desirable for the subscriber at a calling station to initiate a call to another station, station No. 2 for example, the button 2 corresponding to the called station is depressed and then the handset 200 is removed from its support.

Button 2, as indicated in Fig. '7, functions 'to actuate a single code bar Bl, so that the code bar is therefore depressed and causes the common bar 61 to experience a similar operation. As the common bar moves downwardly, it carries with it the projection H (Fig. l'A) and by virtue of the camming action of the button 2, the latching plate I is moved to the right. When the camming portion of the actuated button clears the corresponding hole in plate I05, the spring I01 functions to restore the latch plate I05 to its normal position, causing the depressed button to be locked thereby in its operated position. The projection I22 associated with code bar Bl moves upwardly to operate the springs B causing these springs to separate and thereby remove the short circuit from dry rectifier b. The geared sector 2|9 associated with the common bar 61 pivots on shaft H4 so that its geared end is raised. The pinion gear 4! which meshes with the geared sector 219 is therefore rotated in a counterclockwise direction. The ratchet wheel 42 is similarly rotated and by virtue of the pawl 45 which couples the ratchet wheel 42 and the disc 43, the rotation of the ratchet wheel is communicated to the disc 43.

' The motor spring 202 which couples the discs 43 and 2'2l is wound up due to the rotation of the disc 43, it being understood that the disc 22! which is pinned to shaft 203 is prevented from rotation at this time by the engagement of tripping pawl 220 with the tooth thereof. Thus, incident to the depression of button 2, energy is stored in motor spring 202, andrectifier contact springs F are operated to open position. When the button 2 reaches the limit of its stroke, the geared sector 2|.9 will have been raised to such a position that the latch pawl 55 drops into notch 5'! in the geared sector to maintain the geared sector in its operated position. Thus the geared sector 219 and the depressed button 2 are'locked operated.

Removal of the handset 200 from its support permits springs 201 to operate. Through the linkage consisting of handset button 206 and the pivoted lever I5, the lever arm 19 is depressed causing it and its oppositely projecting arms 80 and BI topivot in a clockwise direction on shaft 28. The member 83 which is integrally formed on the left end, viewing Fig. 5, of arm 8| accordingly moves to cause the tripping member 60 to rotate against the action of spring 0| on shaft 29 in a counter-clockwise direction. pawl 220 which is integral with tripping member 60 is accordingly moved out of engagement with the tooth of disc 22l whereupon the energy stored in motor spring 202 is released and is expended in causing the rotation of shaft 203 with its plurality of cams PI, P2, P3, P0, PON, 231 and 62.

As cam 62 nears its home position, the lobe 63 thereof acts on the lower end of arm 53 causing it to move forwardly, viewing Figs. 2 and 3. The arm 53, as previously described, is the longer right-hand extension of the substantially U- shaped member 52 whose shorter left-hand arm is indicated by the numeral 54 in the drawings. Thus, due to the camming action of the lobe 53 of cam 62 on the arm 53, the arm 54 also is moved forwardly, or more accurately, in a counter-clockwise direction. The pin 58 fixed to the arm 54 therefore functions to lift the latching pawl 55 from the notch 51 in the geared sector 2 I9 thereby ,releasing the geared sector, which, as previously Tripping stated, is integral with the common bar 61. The

spring 66 thenfunctions to restore the common bar to normal and also the actuated code bar Bl.

As the common bar 61 returns to normal, the projection H0 carried thereby moves upwardly to engage, with a camming action, the projection I09 of the latch plate I05. The latch plate is thereupon moved to the right a distance sumcient to permit the depressed button to restore to normal under the action of its associated spring HI.

Operation on conference basis When the handset 200 is completely removed from its support, the position of lever arm 19 relative to that of lever 15 is shown in Fig. 4. This position of lever arm 19 is the same as that occupied by the lever arm when the handset is on its mounting on the telephone set as shown in .Fig. 2. Thus, subsequent to the removal of the handset from its mounting, the mechanism controlled by lever arm 19 is in its normal condition so that when the shaft 203 completes its cycle of rotation, the tripping pawl falls into the notch effected by the tooth on the periphery of disc 22 I, thereby reconditioning the transmitter for a subsequent operation while the handset is still removed from its support.

If, after actuating the button 2, and during the time the connection to the called station is come pleted, the calling subscriber desires to add another station, station No. 3 for example, to. the connection, he may do so by merely actuating button 3 corresponding to station No. 3, and following it with the operation of the reset button RE. When button 3 is depressed, the motor spring 202 is again wound up, it being recalled that with the handset lifted from its support the lever arm 19 assumes its normal position, as shown in Fig. 4, so that the tripping pawl 220 reengages the tooth in disc 22! to hold the disc against rotation during the actuation of the button and the consequent winding up of spring 202. As in the previous case, the geared sector is locked operated when button 3 is fully depressed.

When reset button RE is then actuated, its lower face engages the projection I I2 causing the camming lever H5 to move lever ill inwardly as shown in Fig. 6A, whereupon the tripping pawl 220, through the engagement of the hook-like projection 1 [8 of lever I I1 and the tripping member 60, is lifted out of engagement with the tooth of disc 22I permitting the spring 202 to function to drive the cam shaft 203 through a complete revolution. The cams carried thereby function to transmit the code corresponding to station No. 3, the character of which is determined by the open condition of springs A and D which were actuated by code bars Al and D2, respectively, when the button 3 was depressed.

The reset button RE also serves to permit a subscriber to correct an error resulting from the depression of a wrong station-selecting button before the handset is removed from its support. When a button has been depressed erroneously and the error is detected before the handset is removed from its support, the subscriber merely actuates the reset button RE which releases the code-transmitting mechanism causing it to perform a complet cycle of operation. Obviously, since the signaling circuit is open at the lowermost contacts of springs 20l, no code impulses will be transmitted over the line when the handset is in its position on the telephone set. After the return to normal of the transmitter in the manner previously described, the correct station button may beactuate'd' and the handset removed Circuit operation: call to private branch ea:-

change or central ofiice It will be observed that the line L extending from station No.1 normally extends to a private branch exchange or central oflice by way of the two inner armatures and back contacts of relay 201, link LI and the inner upper and innermost lower armatures and back contacts of cutthrough relay 228. Thus, to extend a call to the private branch exchange, or central office theparty at station No. 1, for example, need only remove the telephone handset 200 from its support to effect the closure of the contact springs 20!. These springs when operated to their closed positions complete the closure of the station loop in a well-known manner and cause thesupervisory relay 204 to operate over the closed loop.

Relay 204 completes an obvious'operating circuit for the slow-torelease relay 205. At its left armature and front contact, relay 205 connects ground potential to conductor 56! and thence over resistance 265 and conductor 244 to the right terminals of the lower windings of relays 24 I, 252 and 253' thereby marking all such relays through which access to station No. 1 is had, busy. This removal of the telephone set at station No. 1 causes the usual line relay to operate at the exchange to bring in a call signal thereat. The call is answered at the exchange in the usual manner. In the case of an automatic exchange dial tone would be connected to the calling line in the wellknown manner.

Should the switchhook or handset button of the telephone set at station No. 1 be accid'ently, momentarily depressed at this time, no permanent loss of the exchange connection results and the calling line will be automatically reconnected to the exchange in the following manner. The opening of the contacts 20| incident to the accidental operation of the button 206 at station No. 1 opens the station loop causing supervisory relay 204 to be deenergized and to release its armature. Relay 205 being slow-to-release remains operated and during the interval in which relay 204 is deenergized, relay 201 operates in a circuit extending from grounded battery, through the Winding of relay 201, armature and front contact of relay 205, upper armature and back contact of relay 208, to ground at the back contact and armature of relay 204. At its outer upper armature and front contact, relay 201 completes a locking circuit for itself independent of the armature and back contact of relay 204. At its inner upper and inner lower armatures and front contacts, relay 201 transfers the calling line L from the link Ll extending to the private branch exchange, or central office to the conductors extending to the alternating current signaling source 209.

Relays H and 2 of the signal receiving and register circuit operate on alternate half cycles of current from the source 209. The operating circuit for relay 2 extends from the right terminal of the secondary winding of transformer 2| 2, through the dry rectifiers 213 and 2 l4, winding of relay 2, front contact and inner lower armature of relay 201, over the ring conductor of the calling line L, over the closed loop at the calling station to the tip conductor of line L, inner upper armature and front contact of relay 207,

toth'e left'terminal of the secondary wind ngs: transformer 2I2. Relay 2!! thus operates on the positive half cycle of current from the source 209. The operating circuit for relay 2H) may be traced similarly except that rectifiers 2|5 and 216 are substituted for rectifiers 2M and 2E3, respectively, and the winding of relay 2H) for the winding of relay 2H. Thus relay 2 operates on the negative half cycles from the source 209.

Ground potential is now extended by way of the outer upper armature of relay 2 and the outer lower armature of relay 2l0 and their respective front contacts, to the innermost upper armatures and back contacts of relays 2| 1 and H8, conductor 2|9, winding of relay 208, to battery and ground. Relay 208 operates in this circuit and at its upper armature and back contact opens the locking circuit for relay 201, which relay deenergizes and restores its armatures, reconnecting the calling line L to the link Ll extending to the exchange. With the release of relay 201 and the consequent opening of the conductors to the signaling current source 209, relays 2H] and 2H release and open the operatingcircuit to relay 208. Relay 208 released, the circuit is restored to the condition it was in prior to the momentary actuation of the switchhook contacts at station No. 1 and the connection between the calling station and the exchange is reestablished.

Replacement of the receiver, or handset at station No. 1 at the termination of the call to the exchange interrupts the station loop in the usual manner, causing the release of relay 204, which in turn, opens the circuit to relay 205. The circuit is then in its normal condition.

Keyed call to station No. 2

When a call is to be initiated at the station No. 1, for example, and intended for the party at station No. 2, for example, to which station the call ing party has direct access, the station-selecting button, or key No. 2 allocated to the called station No. 2, is manually depressed and the telephone handset 200 removed from its support in that sequence. The depression of key No. 2 at station No. 1 causes the operation of code bar Bl as well as the common bar with which the geared sector 2I9 is integrally formed as previously described. The actuated code and common bars are locked in their operated positions. The operation of the geared sector 2I9 causes the motor spring 202 to be wound up, in the manner described, while the transmitter shaft 203 is restrained from rotation due to the engagement of the pawl 220 with the cam 22! which is fixed to shaft 203. The'han'dset when removed from its support trips the pawl 220 and closes the switchhook contacts 20 l. Upon operation of the pawl 220, the cam shaft 203 is caused to rotate receiving the energy stored in the motor spring 202. The shaft 203 makes one complete revolution.

As the cams PON and PO move out of normal positions, the alternate contacts of springs SON function to short-circuit the telephone set and the normal contacts serve to remove the short circuit from the code sending contacts SI S2 and S3. The contacts SO open to maintain the signaling circuit open, it being understood, as will appear presently, that the path for the signal impulses include the contacts SO and requires the closure of these contacts for its completion.

Immediately upon the removal of the handset from its mounting the springs 201 are closed'to complete the closure oflthe station loop circuit in the well-known manner. This loop, in this system includes the normally closed contacts SON. Relay 204 thereupon operates from battery at the exchange and completes an obvious operating circuit for relay 205. Relay 205, operated, marks relays 24!, 252 and 253 and all other relays through which station No. 1 is reached, busy. As the cam shaft 203 starts to rotate, the contacts SON and SO are operated so that the telephone set is short-circuited by the alternate contacts SON and the loop circuit is now open at the contacts SO. During this open interval relay 204 releases and with relay 205 still operated due to its slow-to-release characteristics, relay 20'! operates as previously described and locks to round at its own outer upper armature and front contact by way of the armatur'eancl front contact of relay 205 and the upper armature and back contact of relay 208. Relay 201 performs the same functions ascribed to it hereinbefore, one of which is to connect the signaling current source 209 to the calling line L.

With code bar BI operated in the station set, as described, the spring contacts B controlled thereby will be opened to remove the short circuit from rectifier b. These rectifiers,'however, as well as all other rectifiers a, c, d, e, and f will remain short-circuited until the cam springs S3, S2'and S! are operated by their respective cams P3, P2 and PI. Thus, it will be noted, the code bars selectively prepare certain of the rectifiers a to f, inclusive for effective use in transmitting correspondingly characterized impulses while the cams Pl, P2, and P3 function sequentially to take the characterized impulses and apply them to the line L.

As the cam shaft 203 reaches its first position after one quarter of a revolution,'the pulsing lobe of cam Pl will open the springs SI and'the stud associated with the springs SO will drop into the first notch of cam PO. While this condition maintains, a circuit may be traced for thepositive half cycles from source 209, from the right terminal of the secondary winding of transformer 2l2, rectifiers 2|3 and 2M, winding of relay 2, front contact and inner lower armature of relay 201, ring conductor of line L, closed "contacts SO, contacts S3 and S2 in series, conductor 222, rectifier b from which the short circuit has been r removed by the operation of code bar BI and its associated contact B, normal closed contacts A, conductor 223, alternate contacts SON, tip conductor of line L, inner upper armature and front contact of relay 201, to the left terminal of theprimary of transformer 2l2.- It will be noted that no path exists at this time for the negative half cycles so that only relay 2 perates and relay 2|!) remains unoperated.

At its inner lower armature and front contact, relay 2 connects ground to conductor'224 to maintain relay 205 operated. At its inner upper armature and front contact, relay 2 completes a circuit for the energization of rela I+ which extends from grounded battery 225, conductor 226, winding of relay conductor 221, back contacts and outermost upper armatures of relays 2 l8 and 2 ll, inner upper armature and front contact of relay 2| to ground. Relay I+ operates in this circuit'and locks to ground at the back contact and outer lower armature of relay 208, byway of its own left armature and front contact and conductor 229: At its outer lower armature and front contact, relay 2 establishes a circuit Iprthe .upper winding of relay 2l8i-which may be traced from grounded battery, upper or'primary winding of relay 2i8, back contacts and outer lower armatures of relays M8 and 2H, to ground by way of the outer lower armature and front contact of relay 2. Relay 2|0 operates partially at this time and connects its lower or secondary winding in series with its primary winding to ground at the outer lower armature and front contact of relay 201. Relay 2l8 is prevented from full operation at this time as its secondary winding is short-circuited by the outer lower armature and front contact of relay 2. Thus, upon the transmission of the positive impulse resulting from the opening of pulsing springs SI which occurs when the shaft 203 makes the first quarter of a complete revolution, relay l+ operated and locked to the relay 208, as described. I

As the cam shaft 203 continues to rotate under the action of motor spring 202, the cams carried thereby move out of their first positions and advance to their second positions. The stud associated with the contact springs SO moves out of the notch l in cam PO to cause the opening of the contact springs SO; Similarly the contacts SI controlled by cam P! are reclosed. With the opening of the contacts springs SO the signaling circuit to the'source209 is opened and relay 21! is deenergized. Relay 2 I l accordingly releases its armatures. In releasing its outer lower armature relay 2l I removes the short circuit from the lower or secondary winding of relay 218 thereby permitting this relay to operate fully. At its three 'upper. armatures relay 2|8 transfers the and i leads from the first set of directional relays l+ and I, to the second set of directional relays 2+, 2 and 2:. It will'be noted at thls time that the first set of directional relays consists of but two relays while the remaining two sets of directional relays each consists of three relays. This is due tothe fact that the first component of each of the possible code signals is made up of either a positive or a negative current impulse and never includes both polarities. This is apparent from the chart shown'in Fig. 9. The second and third components however may; as shown, in the chart, each consist of a positive impulse, a negative impulse, or a combination of both polarities and therefore require three directiona1 relays for registering such impulses.

As the cam shaft 203 reaches its second position the stud associated with the springs SO drops into the notch 2 in cam PO and simultaneously the pulsing lobe of cam P2 functions to separate the contact springs S2. The closure of the contacts SO reestablishes the continuity of the signaling loop and the contacts S2, in their operated condition remove the short circuit from the second pair of rectifiers c and cl. As neither of the contacts 0. and D has been operated by the code bar Bl, the rectifiers c and d are still short-circuitedon the transmitter side so that both half cycles from the source 200 will traverse the signaling path. Both relays 2l0 and 2 will therefore operate at this time. The circuit for relay 2| 0 extends from the left terminal of the secondary winding of transformer 24 2, over the front contact and'inner upper armature of relay 201, tip conductor of line L,.alternate contacts of springs SON, closed cam contacts SI conductor 222, contacts C and D, conductor 233, closed contacts S3 and SO; ring conductor of line L, inner lower armature and front contact of relay 201, rectifier 2|6, winding of relay 2l0, rectifier 2l5, to the :right terminal of the secondary of transformer 2|2. The circuit for relay 2|| may be traced from the right terminal of the secondary winding of transformer 2|2, rectifiers 2 3 and 2M, winding of relay 2, front contact and inner lower armature of relay 201, ring conductor of line L, spring contacts SO and S3, conductor 233, contacts D and C, conductor 222, spring contacts SI, alternate contacts SON, tip'conductor of line L, inner upper armature and front contact of relay 201, to the left terminal of the secondary of transformer 2|2.

Relay 2|0, at its inner upper armature and front contact, and relay 2| at its inner lower armature and front contact reconnect ground to the winding of slow-to-release relay 205 to insure this relay being held operated. With both relays 2|0 and 2H operated, a circuit may be traced from ground, outer upper armature and front contact of relay 2||, front contact and outer lower armature of relay 2|0, innermost upper armature and back contact of relay 2|l, innermost upper armature and front contact of relay 2|8 (held operated to ground at the outer lower armature and front contact of relay 201), winding of relay 2:, conductor 226 to grounded battery 225. Relay 2: operates in this circuit and. locks to ground on conductor 229 by way of its left armature and front contact.

At the outer upper armature and front contact of relay 2|0 and the outer lower armature and front contact of relay 2 a circuit is completed from ground, over the outer lower armature and back contact of relay 2|I, outer lower armature and front contact of relay 2|8, to battery and ground, through the upper, or primary winding of relay 2H. Relay 2 ll partially operates in this circuit and at its inner lower armature and front contact connects its secondary, or lower winding in series with its upper winding to ground at the outer lower armature and front contact of relay 201. Relay 2|'| does not fully operate at this time because its secondary winding has ground potential applied to both terminals thereof. Thus, as a result of the transmission of the second component of the code signal relay 2: is operated and locked.

As the cam shaft 203 continues its rotation, the cams carried thereby move out of their second positions. As the cam PO moves out of the second position the stud associated with the contacts S is moved out of notch 2 in cam PO causing the contacts S0 'to separate and war the signaling circuit. With the signaling circuit open, the relays 2|0 and 2| I are deenergized and release their armatures. Thus, the short circuit is removed from the secondary winding of relay 2|I allowing this relay to fully operate to ground at the outer lower armature and front contact of relay 201.

Relay 2H, at its three upper armatures transfers the and leads from the second set of directional relays 2+, 2-.-, and 2:, to the third set of directional relays 3+, 3-, and 3:.

As the cam shaft 203 reaches itsthird position the (stud associated with springs SO falls into notch 3 of cam PO causing the reclosure of springs SO and reestablishing the continuity of the signaling circuit. Simultaneously, the pulsing lobe of cam P3 operates springs S3 causing them to separate and to thereby remove the short circuit from the line side of rectifiers e and 1. However, since neither contacts E nor F has been actuated by the code bar Bl, these rectifiers are still short-circuited on their transmitter side. Neitherhalf wave of the alternating current is therefore blocked and both half waves traverse the now closed, signaling circuit to cause the reoperation of both relays 2|0: and 2| i. The cincuit of relay 2| |i s tracedcfrom the right terminal of the secondary windingof transformer 2|2', rectifiers2|3 and 2M, winding of, relay 2| l, front contact and inner lower armature of relay 2,01, ring conductor of line L, contact springs SQ, conductor 234, contacts F and E, conductor 233', contact springs S2 and SI, alternate contacts SON, tip conductor of line L, inner upper armature andfront contact of relay 201, to the left terminal of the secondary of transformer 2|2. The circuit for relay 2|0 extends fromthe left terminal of the secondary of transformer 2|2, over the front contact and inner upper armature of. relay 201, thence over the tip conductor of line L, alternate contacts SON, contact springs SI and S2, conductor 233, contacts E and F, conductor 234, contacts S0, to the ring conductors of the line, inner lower armature and front contactof relay 201, rectifier 2|6, winding of relay 2|0, rectifier 2|5, to the right terminal of the secondary winding of transformer 2|2.

With both relays 2|0,and 2|| operated, directional relay 3: operates in a circuit traced from grounded battery 225, conductor 226, winding of relay 3:, front contact and innermost lower armature of relay 2H, outer lower armature and front contact of relay 2|0, front contact and outer upper armature of relay 2|| to ground. Relay 3: operated, locks to ground onconductor 229.

Itwill be noted at this time that when both half waves of signaling current are transmitted as the second and third components of a signal code, not only do directional relays 2: and 3: operate, but relays 2+, 2, and 3+ and 3- will operate. However, it will be observed that when either relay 2+ or relay 3+ is operated the circuits to the armatures 2+, 2-, or 3+ and 3- are opened so that the operation of relays 2+ and, 2- simultaneously with relay 2:, or the operation of relays 3+ and 3 simultaneously with relay 3: do not complete any line connecting circuits other than the one circuit controlled by either, or both relay 2: and relay 3:. In the case-just described therefore, through relays 2+, 2+, 3+ and 3-. operate, they do not function to effect a line circuit selection.

Relay 235 now partially operates in a circuit traced from grounded battery, upper or primary winding of relay 235, from contact and outer lower armature of relay 2|'|, to ground by way of the outer upper armature and front contact and the outer lower armature and front contact of relays 2|0 and 2| respectively. In operating, relay 235 connects itslower, or secondary winding in series with its upper, or primary winding to ground at the outer lower armature and front contact of relay 201; Relay 235 is prevented from further operation asits secondary winding is short-circuited.

When shaft 203 moves out of the third position, the contact springs SO are again separated to open the signaling circuit. Relays H0 and 2|! accordingly, are deenergized and release their armatures. Upon release of relays 2| 0 and 2H, the short circuit is removed from the secondary winding of relay 235 whereupon this relay fully operates under control of relay 201'.

As a result of the transmission of the three components of the signal code which identifies the called station No. 2, directional relays 2: and 3:, are operated and'locked to ground 21" under control of relay 208. The signal code which identifies station No. 2 is made up of three components, a positive impulse and two impulses of both positive and negative polarities as indicated byv the chart in Fig. 9. These components were 1 selectively derived from the source 209 by the operation ofcode bar Bl incident to the actuation of the No. 2 key at the calling station. The three components were sequentially transmitted through the media of contact springs Si, S2 and S3. respectively controlled by cams PI, P2 and P3 carried by the shaft 203.

. When the shaft 203 reaches its home position, the spring 235 engages the fiat surface of cam 231 carried bythe shaft 203. In its home position the-notch in cam PON again receives the stud associated with the springs SON to further insure the shaft coming to rest in its home position and also to reconnect the calling substation to the line L and to remove the short circuit thereof which was maintained during the signaling interval by the alternate contacts SON. Thus, the signal transmitter and the calling station circuit are restored to normal condition, it being understood that when the shaft 203 reaches its home position the actuated code bar BI is restored to normal position as previously described] .YWith directional relays l+, 2: and 3: operated and locked under control of relay 208 the following circuit is established: from ground at the front contact and outer lower armature of relay 201, both armatures and front contacts of relay 235, winding of busy test relay 240, right armatureand front contact of relay l+, inner right armature and front contact of relay 2:, innermostright armature and front contact of relay 3:, conductor 230, upper 1-2 winding of relay 2, to battery and ground by way of conductors 290, 211 and resistance 29!. Relay 241 if the called line is busy, does not operate in this circuit as will appear from the following description. It will be noted that battery for the energization of the connecting relay, such as relay 24l is associated with the line circuit of the called station, such as line circuit No. 2.

Called station busy 22.. operates, it shunts the combinationof thermistor 245 in series with the relay, with the resistance 241. The resulting current is suflicient to hold relay 246 operated but not enough to hold down the resistance of the thermistor 245. This resistance rises in about .25 second to a value that reduces the current through relay 246 to a value that allows the relay to release and disconnect If the line extending to called station No. 2 is busy the connector relay 243 associated therewith will be operated. If operated, relay 243 at its outer upper armature and front contact connects ground potential to conductor 216 and thence, by way of resistance 304, to the conductor 211 which, as indicated in the preceding paragraph is connected to the left terminal of the 1-2 winding of relay 241 and to corresponding windings of similar relays associated with line No. 2 such as windings 3-2 and 4-2 of relays 332 and 348, by way of conductor 290. Thus, with ground potential connected to both sides of the winding 1-2 of relay 24 l this relay will not operate.

The circuit previously traced as extending from the armatures of relay 235 throughthe winding of relay 240 also extends through resistance 345, thermistor 245, winding of relay 246, to battery and ground. Thus, if the called line is busy, relays 240 and MI do not operate but, in about .3 second, the time required to heat thermistor 245 to a temperature which will permit sufiicient current to traverse the winding of relay 246, relay 246 operates. At its middle upper armature, relay 246 connects a source of busy tone current BT to the calling line No. 1 over the ring conductor thereof. 7 g;Relay 246 is self-interrupting, that is,.when it the busy tone from the calling'line. The relay again operates slowly through the thermistor but not quite as slowly as the original operate period due to the fact that the thermistor does not cool down to the ambient temperature. At the same time that relay 240 connected busy tone to the calling line, it connected ground at its outermost upper armature and front contact through the thermistor 248 to the lower winding of relay 228. After approximately four operations of relay 246, the resistance of thermistor 248 drops to the point at which sufficient current flows through the lower winding of relay 228, by Way of conductor 305, to cause relay 228 to operate.

Relay 228 operated, extends the link Ll of line circuit No. 1 to battery and ground through the windings of line relay 249 which relay will operate when relay 201 releases to extend the link Ll' to the line circuit L of the calling line as will 7 now be described.

'It will be recalled that slow-to-release relay 205 was held operated during the pulsing period under the control of relay 210 or relay 2| I or under control of both, depending upon the code transmitted. When the code transmitting period is terminated relay 205 releases and opens the locking circuit to rela 201. Relay 201, released, connects the line L to link Ll so that line relay 249 is now connected across the established connection and will operate over the closed line loop at station No. 1.

It is to be noted at this time that the armature and contact arrangement of relay 201 is such that when relay 201 is released the continuity of the tip and ring conductors of line L and link Ll is reestablished before the outer lower armature of relay 201 removes ground potential from its front contact. Furthermore, relay 208 is slow to operate. Therefore when relay 249 operates it connects ground by way of its inner lower armature to the hold conductor 260 before the ground at the. outer lower armature and front contact of relay 201 is removed from conductor 230. Thus, the relays which operated on the application of ground to conductor 230 are now held operated to ground under control of line relay 249.

At its outer lower armature and front contact relay 249 connects ground to conductor 558, then over the front contact and middle lower armature of relay228, conductor 250, to battery and ground through the winding of relay 208. Relay 208 operates and at its outer lower armature and back contact opens the locking circuit for the operated directional relays, which relays then restore to normal.

When relay 201 released, as described, the looking circuit to relays 2H, 2! and 235 is opened and these relays restore their armatures. If desirable, the calling party may recall station No. 2 by again depressing the No. 2 button, followed by the depression of the reset button RE, to cause the code transmitter to again transmit the code corresponding to the called station No. 2. The circuit operations under this condition are the same as described hereinbefore in connection with the initiation of a call at station No. 1 and directed towards station No. 2. If, on a recall,

No. I is restored to its mounting causing relay 228 to release. Relay 208 also releases when relay 249 restores its armatures.

Completion of keyed call to station No.2

If the called line is idle there will be no direct ground connected to the left terminal of the 1-2 winding of relay 241 as previously indicated. Under this condition relays 240 and 24! will operate in a circuit extending from grounded battery associated with the line circuit No. 2, resistance 29 l, conductors 211 and 29!], upper 1-2 winding of relay 24 I, conductor 230, front contact and innermost right armature of directional relay 3:, front contact and inner right armature of directional relay 2:, front contact and right armature of directional relay Ii, Winding of relay 240, front contacts and armaturesof relay 235, outer lower armature and front contact of relay 201 to ground. Relay 24!! operates immediately in this circuit and at its upper armature and front contact connects resistance 255 in shunt with its own Winding thereby increasing the'flow of current in the circuit previously traced to a value sufficient to cause relay 24! to operate. At its lower armature and back contact, relay 24!! opens the operating circuit of relay 246.

With relay 24] operated, ground on conductor 236 is extended over the upper double make contacts of relay 24! to conductor 260 and resistance 253 and theme in parallel to battery and ground through the upper winding of relay 262 and the lower winding of relay 228, the latter parallel branch including conductor 361. Relays 262 and 228 operate in these circuits.

The ground on conductor 230 is also extended over the upper double make contacts and outer upper armature of relay 24! to conductor 261 and thence over two parallel branches, one by way of conductor 213 and the upper winding of relay 243, and the other by way of conductor 251, the armature and back contact of relay 268 of line circuit No. 2, resistance 269, thermistor 216, winding of relay 21!, to battery and ground. Relays 243 and 268 operate in these circuits.

As a consequence of the application of ground to the conductor 256, connecting relay 24!, cut through relays 228 and 243, relay 262 of line circuit No. 1 and ringing relay 211 of line circuit No. 2 are operated and it will be described presently how these relays lock operated under control of line relay 259 of line circuit No, 1.

It has been described hereinbefore how, after the completion of the code transmitting period, relay 205 releases its armature to cause relay 201 to be deenergized. With relay 261 released, the calling line L is extended to the link Ll, so that, with relay 223-operated, as described, line relay 249 operates over the closed line loop. Relay 208 operates, in the manner described hereinbefore, to release the operated directional relays, and relay 201 operated, releases relays 21 1, 218 and 235.

Relay 248at its inner lower armatureand front contact connects ground to conductor 381 to hold relay 228 operated. It also connects ground over resistance 263 and conductor 260, which ground, in effect, replaces the ground on conductor 230 so that relays 24!, 243 and 2H are now held operated under'control of relay 249 as is also relay Relax/ 228 at its=outer upper armature and front contact connects ground potential to conductor 56f, resistance 265', conductor 244 and thence in multiple to the right terminals of the lower windings of relays 241, 252 and 253 and of all similar relays by means of which the station No. 1 may bereached from all other stations of the system. Inthis manner the calling line is marked busy to all other lines of the system. Similarly, when relay 243 operates its outer upper armature, ground is extended over conductor 216, resistance 304, conductor 211, and thence in multiple to the right terminals of the lower windings of relays 332 and 348 and of all other similar relays by means of which the station No. 2 may be reached from all other stations of the system. Thus the busy condition of the called station No. 2 is made evident.

Relay 262 of line circuit No. 1, operated, opens the operating circuit to the ringing relay 264 to prevent ringing current being connected to the calling line.

Relay 241' at its inner upper and lower armatures and front contacts connects the tip and ring conductors 2'56 and 251 of line circuit-No. 1 to corresponding conductors 556 and 551 of line circuit No. 2.

Relay 243 at its inner upper and innermost lower armatures and front contacts extends the tip and ring conductors 214 and 215 of line circuit No. 2 to corresponding conductors of the called line 2L of station No. 2 by way of corresponding conductors of link L12,

Relay 21! operates slowly, in the circuit previously traced, owing to the interval of time re quired by the thermistor 218 to heat sufficiently to allow adequate current to pass through the Winding of relay. Relay 21l at its lowerand outer upper armatures and front contacts connects the signaling current source 212 to the tip and ring conductors 214 and 215 towards the called station No. 2 and since relay 243 is operated and a relay, corresponding to relay 261 (Fig. 12) and associated with the line 2L of the called station is unoperated, this signaling current functions to operate the ringer at station No. 2 in the well-known manner, Relay 21! operates in the same manner as did relay 246' previously described so that it functions to apply signaling currentv to the called line intermittently and thus simulate machine ringing. By virtue of the combination of elements 210, 21l and 563 simulated machine ringing is'derived from the alternating current source 212, and immediatel-y upon the operation of the ringing relay the ringer at the called station is activated thus eliminating the delay in the ringer operation prevalent in systems using: an interrupted ringing supply should the ringing relay operate on the silent interval.

Party at called station No. 2 answers When the party at called station-No. 2 responds to the operation of the. ringer at station No. 2

and removes the handset from itsv support, line relay- 289 of line circuit'No, 2 operates,- on the silent interval of the ringing," cycle, over the closed loop at the called station. Relay 280, operated, causes" relay 258 to operate in an obvious circuit. Relay 268' opens: the operating. circuit to relay 2H and locks in a'circuit whichmay be traced from battery and ground, l'owerwinding of relay 288, conductors: 26!" and 261, outer upper armature and frontcontact of relay 2'41, conductor 26D, resistance263', front contact and inner lower armature of relay 249 to ground. Relay 21!, released, disconnects the ringing current source 21 2 from 

